Supporting the rotational shafts of such apparatus as motors, turbines and pumps, by ball bearings is well known. The impeller shafts of turbopumps employed in rocket engines are typically cooled by a flow of liquified (cryogenic) rocket propellant such as liquid oxygen or liquid hydrogen. Because such liquified fuels provide little, if any, lubricity, in such applications, it has been the practice to lubricate the ball bearings by sacrificially removing dry lubricant from the cage: the component which holds the balls, and depositing this lubricant by means of the balls onto the races in which the balls roll. The cage comprises hollow elements containing the lubricant, which accommodate the balls, attached to a metal shroud as by riveting. To minimize wear on the cage due to rubbing of the cage on the races as a result of high speed operation (tens of thousands of revolutions per minute) the cages are, for the most part, piloted on the inner race. That is, the inner race is provided with lands thereon, the cage being maintained in overall alignment with the bearing components by an extremely close fit with those lands. When a cage is piloted on an inner race in this manner, normal removal of cage material occurs, due to rubbing of the cage on the inner race lands. Factors such as cage weight, balance, orbital speed and land clearance as well as ball-to-cage loads, friction factors, coolant flow rates and coolant physical properties can contribute to such rub wear of the cage on the inner race lands which creates a very unstable condition. Such an instability occurs because cage wear removes material from the cage which further contributes to cage imbalances, thereby resulting in still further cage wear and still further imbalances and rubbing.
In an attempt to overcome the shortcomings of high cage wear rates in prior art cryogenic ball bearings, lighter weight shrouds have been employed in the cages to reduce centrifugal loading and rub wear, clearances between guide lands on the inner races and cage have been reduced to reduce rub forces, cages have been balanced with greater precision to enhance balance, and flow rates of coolant have been adjusted in an attempt to optimize the fluid dynamic forces associated therewith. However, while such modifications to prior art bearings have met with some success in increasing the life span of the bearing cages, they have not enabled prior art bearings to enjoy life spans long enough to render the bearings useful in multiple launch rocket engines anticipated in future commercial and military space vehicle and satellite launches.